Scattered to gregarious among needles under coastal scrub of Juniperus communis. Occasionally solitarily on small Juniperus twigs. Also recorded from alpine Salix scrub. Late autumn. Rare or possibly overlooked. So far only recorded from Greenland, Norway, Sweden and Spain (Cifuentes et al. 2024).

Pileus 6-12(-21) mm across, cylindrical or more or less hemispherical when young, then conical or obtusely conical to parabolical, occasionally with a small umbo; translucent-striate, sulcate, dry, glabrous; pale yellow to greenish yellow or olivaceous with almost no yellow components, or olivaceous centre with paler, yellowish margin; drying to pale yellow all over. Lamellae 12-19 reaching the stipe, ascending, narrowly adnate, occasionally with a short decurrent tooth, becoming slightly intervenose with age; yellowish to cream coloured or pale grey to white, with the edge concolorous. Stipe 50-65 x 1-1.5 mm, straight to somewhat flexuous, often curved towards the base, firm, terete, equal, glabrous except for the pruinose apex; the apex whitish or pale grey, darker grey to brownish below, occasionally with a yellow component; the base densely covered with long, coarse, flexuous, whitish fibrils. Odour not distinct. Taste not recorded.

Basidia 30-36 x 6.5-8 µm, clavate, 2-spored, more rarely 1-spored, with sterigmata 8-9 µm long. Spores 8.5-11.2 x 6.2-8.2 µm, Q 1.2-1.6, Qav ~ 1.4, smooth, broadly pip-shaped, amyloid. Cheilocystidia 15-40 x 6.5-17 µm, forming a sterile band, clavate, covered with unevenly spaced, fairly coarse, simple, cylindrical, straight to curved excrescences 1.5-8(-20) x 0.9-2 µm, some with a somewhat swollen tip. Pleurocystidia absent. Lamellar trama vinescent in Melzer's reagent. Hyphae of the pileipellis 2.5-3.5 µm wide, densely covered with simple to furcate, cylindrical excrescences 2-4.5 x 0.5-1 µm, somewhat gelatinized. Hyphae of the cortical layer of the stipe 1-2.5 µm wide, covered with simple, cylindrical excrescences 1-6.5 x 0.9-1.3 µm. Clamps absent, or with some +/- abortive clamps (but see remark below).

Microphoto of cheilocystidia

Microphotos of cheilocystidia and hyphae of the pileipellis

Mycena citrinovirens was originally described from Greenland in 1955. It has been found regularly in two Norwegian localities since 1988 (Aronsen 1994). Maas Geesteranus (1991) placed it in sect. Mycena, but Aronsen & Læssøe (2016) pointed out that in some features it shows a closer relation to sect. Filipedes. This was confirmed by Cifuentes et al. (2024), based on a phylogenetic analysis. It can be distinguished from members of both section Mycena and Filipedes on account of the small size, the yellowish colours in the pileus, and the typical growth on Juniperus needles. In the field it may be confused with Mycena citrinomarginata, but that species can easily be distinguished because of its smooth, lageniform cheilocystidia.

The phylogenetic analysis performed by Cifuentes et al. (2024) showed that M. citrinovirens clusters in a clade together with Mycena xantholeuca Kühner. It is interesting that both species have cheilocystidia where some of the excrescences have swollen tips. M. xantholeuca generally has a larger pileus (5-30 mm), a more whitish colour, more lamellae reaching the stipe (16-34), a whitish stipe, 4-spored basidia, and more elongated spores (Qav 1.7).

The holotype of M. citrinovirens has 2-spored basidia and is devoid of clamps but the Norwegian collections, equally 2-spored, have some clamps in all tissues, of which many are +/- abortive. Cifuentes et al. (2024) studied two collections from Spain, which had 2-spored basidia but possessed clamps in all tissues. This is another example that presence of clamps may not have such high taxonomic value as was claimed by Maas Geesteranus (1978).

The Norwegian collections generally are fairly small, with a pileus less than 10 mm, but one collection from 2006 had a pileus measuring up to 21 mm across.

See Mycena citrinovirens paper.